Resistor unit



Patented Nov. 12, 1940 PATENT OFFICE RESISTOR UNIT Charles J. Ganci, Ridgewood, N. Y., assignor to Ward Leonard Electric Company, a corpora tion of New York Application March 16, 1939, Serial No. 262,093

4 Claims.

. This invention relates to resistor units particularly of .the non-inductive type for use in alternating current circuits.

Such units are desirable for various purposes 5 in requirements from comparatively low resistances to high resistances such as 5000 to 10,000 ohms. It is also desirable for non-inductive requirements that the'approach to noninductivity should be asclose as possible and that variations in duplicate units should be reduced to a minimum. This can best be accom- .plished by machine wound units wherein the pitch is maintained uniform and the number of turns made the same for each duplicate.

One way of making a non-inductive unit is to provide two windings connected in parallel and wound in opposite directions on their support. But when it is attempted to accomplish this by applying the winding to a tubular support for obtaining the convenience and advantages of a machine wound unit, the variations in the windings even when carefully done are so great that there is a considerable lack of uniformity between units and a failure to approach a high degree of non-inductlvity. The poor results obtained are due to the fact that when the reverse winding is applied over. the first winding,

the second winding tends to follow the turns of the first at cross-overs and then jumps over the 80 first winding at varying points, some of the turns lumping sooner and some jumping later and these variations cause further variations in successive turns. The result is a more or less mixture of irregularities and variations and lack of 85 uniformity in results. The use of tubes as supports for such windings therefore seemed totally unavailable for obtaining uniform rusults.

However, the advantages in the use of tubes as supports for such windings are obtained by 40 the present invention and the above mentioned difficulties overcome and a highly desirable noninductive unit obtained with substantially uniform results. This is accomplished by flattening two sides of the tube sufficiently for insuring 45 proper fiat surfaces on which the cross-overs may be properly made without any-tendency of the turns of the second winding to follow the turns of the first winding and yet avoiding the provision of flat surfaces of too great a width. 50 The latter conditionleads to various difilculties when the unit is machine wound, such as breakage of the resistive conductor under too great a strain and shock when making the turns at 'the' corners, variations in the winding' due to 66 the long stretch over wide fiat surfaces, breakage of the support and inability to wind the turns with a small pitch for the making of high resistance units. Other difficulties arise with too wide fiat surfaces when attempting to coat the unit with an insulating coating such as 5 vitreous enamel. The curing of the coating, such as in the firing of a coating of vitreous enamel material, causes expansions and contractions of the parts relatively to each other and a so-called "swimming of the turns of the 10 conductors. This changes the relativepositions of that portion of the turns on the flat surface, changes the uniformity of cross-over points even if properly previously made, introduces short circuits at some points between turns and 15 not only alters the resistance of the unit but gives'varying results as regards the non-inductance of the unit. By the present invention all of the foregoing difiiculties and objections are overcome. 20

One object of the present invention is to provide a resistor unit which shall closely approach non-inductivity. Another object is to provide a form of structure which will permit a close approach to uniformity in results attained and 25 in duplication of units. Another object is to provide a form of structure. which will permit machine winding of the conductors on the support with the convenience, speed and uniformity obtained thereby. Another object is to provide 'a form of unit which will permit the application and curing of an insulating coating without materially aflecting the position of the individual turns or the inductance or resistance of the unit. Another object is to obtain units of high resistance by permitting the use of fine wires and the adjacent turns of which may be close to each other. Other objects and advantages will be understood from the accompanying drawing showing one embodiment of the in- 40 vention.

Fig. 1 is a plan view of a tube showing one winding applied thereto; Fig. 2 is an end view;

Fig. 3 is a view similar to Fig. 1 showing the relation of the second winding to the tube when applied; Fig. 4 is a similar view showing the second winding applied over the first winding; and Fig. 5 is a similar view after the application of the insulating coating.

The support of the unit is shown as a tube I of insulating material such as porcelain. Two opposite exterior sides 2,0f the tube are flattened and in the tube illustrated the angle subtended by the chord of each of these flat surfaces is 60". This gives a very desirable relation be-Jl that the turns of tween the extent of the rounded portions of the tube and the flat surfaces for obtaining the desirable results and for overcoming the difficulties already referred to. In some cases the angle of this chord may be as much as 90 and as low as with advantageous results.

At each end of the tube is shown a terminal band 3, in this instance formed of a flexible stranded wire encircling the tube and having its ends twisted together as shown at 4 for forming terminal leads. At points opposite these leads are small angular metal lugs 5 having one end positioned under each band and soldered thereto. The outer end of each of these lugs is notched to receive a few turns of the resistive conductor for making electrical connection thereto, the connection being soldered after completion of the-winding.

Referring to Fig. 1 the resistive conductor 6 of the first winding is shown wound around the tube with a certain pitch and inclination de termined by the pitch of the winding apparatus. One end of the conductor is first given a few turns around the outer portion of the left-hand lug 5 and the tube is rotated while the conductor is fed from the device which gives the desired pitch. When the conductor reaches the right-hand terminal band, it is given a few turns around the outer portion of the righthand lug 5 for making connection thereto. The direction of rotation of the tube and movement of the device which feeds the conductor at a definite pitch is then reversed and the conductor is then wound back over the first conductor layer. Fig. 3 shows the relation of the second layer 1 of the conductor to the tube; and Fig. 4 shows the second layer 1 of the conductor as applied over the first layer 6. The remaining end of the conductor is fastened to the left-hand lug 5 by giving it a few'turns around it. After the conductor connections to the lugs are soldered, the outside of the tube is coated with insulating material and cured. This is preferably a vitreous enamel material 8 which is vitrified by firing in a furnace, giving a final product as shown in Fig. 5

The result is a unit composed of two reversely wound windings connected in parallel with the windings symmetrically located with reference to each other giving a resistance unit having very small inductance.

Referring to Fig. 4 it will be noted that the cross-over points of junction between the turns of the two layers are all on a line parallel with the axis of the tube, there being no irregularities in these points or in the spacing of the turns and such a condition is desirable for reducing the inductance to a minimum. The width of the flat surfaces of the tube must be enough to insure the resistive conductor are definitely spaced from each other at the edges between the fiat surfaces and the rounded surfaces and must also be enough to insure that when the conductor of the second layer is brought down on the flat surface it will lay over and cross the conductor of the first layer at the middle line of the flat surface and not have any tendency to run along with or follow a turn of the first layer. Furthermore the width of the flat surfaces cannot be too great owing to the disadvantages already referred to and also because if the rounded portion of the tube is not wide enough the machine winding of the conductor cannot be properly carried out .owing to there not being suflicient rounded surface to give a smooth feeding of the conductor or a sufficient holding surface on the rounded portion for guiding and maintaining the layers in their proper definite positions. The edges formed by the meeting of the flat surfaces and the round surfaces provide a series of points at which the conductor is bent and thereby form fixed points of anchorage of the conductor during the winding operation and after the winding is completed. This aids in overcoming any tendency of the conductor to shift its position.

Although a particular embodiment of the invention has been described, it will be apparent that various modifications may be made without departing from the scope of the invention. Although a tube has been described as the support, a solid cylinder may sometimes be used. Also instead of the opposite surfaces being flat they may be slightly convex or concave and still obtain the advantages of the invention. Likewise the opposite rounded surfaces need not conform strictly to the arc of a circle and such variations and others may be made within the scope of this invention.

I claim:

1. A resistor unit comprising a round support and a resistive conductor wound thereon in two layers in reverse directions, said support having oppositely located longitudinally extending flattened surfaces whereon the turns of the outer layer cross over the turns of the inner layer and wherein the chord of the flattened surfaces does not subtend an angle greater than 90 or less than 30.

2. A resistor unit comprising a round support and a resistive conductor wound thereon in two layers in reverse directions, said support having oppositely located longitudinally extending flattened surfaces whereon the turns of the outer layer cross over the turns of the inner layer, and wherein the chord of the flattened surfaces does not subtend an angle greater than 90 or less than 30, and a vitreous enamel coating covering said two layers of the conductor.

3. A resistor unit comprising a round support and a resistive conductor wound thereon in two layers in reverse directions, said support having oppositely located longitudinally extending flattened surfaces whereon the turns of the outer layer cross over the turns of the inner layer, and wherein the chord of the flattened surfaces does not subtend an angle greater than 90 or less than 30, the curved portions of the support and the flattened portions meeting to form edges at which the conductor is bent.

4. A resistor unit comprising a round support and a resistive conductor wound thereon in two layers in reverse directions, said support havingoppositely located longitudinally extending flattened surfaces whereon the turns of the outer layer cross over the turns of the inner layer, and wherein the chord of the flattened surfaces does not subtend. an angle greater than 90 or less than 30, the curved portions of the support and the flattened portions meeting to form edges at which the conductor is bent, the pitch of the turns of the two layers being the same and the cross-over points being along a line parallel to the axis of the support.

CHARLES J. GANC'I. 

